The present invention relates to a device for butt welding pipes. In the present context, the term xe2x80x9coscillation frequencyxe2x80x9d denotes the number of oscillations of the torch in a predetermined linear unit of movement (for example, one inch) of the carriage along the guide strip.
In known devices of the type mentioned above, the movement means capable of imparting an oscillatory motion to the welding torch are of the type comprising an electric motor connected to a cam, or a pneumatic piston; both of these solutions present problems.
As is known to persons skilled in the art, in order to carry out the butt welding of two pipes it is necessary to make numerous welding passes, during which a plurality of superimposed layers of weld material are deposited in the groove delimited by the two joined ends to be welded.
In some of these welding passes it is preferable to impart an oscillation to the welding torch, in such a way as to distribute the weld material uniformly in the groove when the distance between the walls of the groove varies.
In the known devices having torch moving means of the cam type, the position of the cam has to be regulated for each type of pass. The operations for regulating the position of the cam are relatively lengthy and complicated, and, if they are not carried out in a very accurate way, cause irregularities in the welds.
Numerous problems are also present in devices in which the oscillatory movements are produced by a pneumatic piston. In the first place, the system is bulky, and requires a relatively complicated pneumatic circuit and a dedicated control unit. Furthermore, the carriage has to be connected by a tube to a source of compressed air. The regulation of the amplitude and frequency of oscillation takes place manually by the operation, respectively, of a handle connected to a screw capable of limiting the movement of the torch and a vent valve of the piston.
In these devices also, for each welding pass it is necessary to carry out a relatively lengthy and complicated operation of manual regulation of the oscillation means, which must be carried out with great accuracy. For these reasons, machines with these forms of regulation of the oscillation characteristics of the torch are normally regulated to carry out one type of pass, and continue to be used subsequently to execute this specific pass. This means that it is necessary to have a number of machines to complete one weld.
The object of the present invention is to provide a device for butt welding pipes, which makes it possible to regulate in a simple, fast and reliable way the frequency and amplitude of oscillation and the speed of oscillation of a welding torch, and which is capable of ensuring constant conformity with the aforesaid parameters once they have been set.
A further object is that of providing a device which makes it possible to regulate the characteristic values of the oscillation of the welding torch in accordance with the speed of travel of the device on the guide strip.
A further object is that of providing a device in which the means for oscillating the torch and for controlling this oscillation are compact and easily assembled.
A further object is that of providing a device which does not require manual regulation of the oscillation means during the various welding passes.
A further object is that of providing a device which makes it possible to start and finish the welding with the welding torch in a predetermined position with respect to the center of the weld.
A further object is that of providing a device which makes it possible to carry out welding with non-symmetrical oscillation of the torch.
A further object is that of providing a device which makes it possible to vary the stop times of the torch at the limits of the oscillation so that welds can be carried out with a distribution of the weld material having a particular geometrical form, for example flat, concave, convex or undulating.
A further object is that of providing a device in which the operator can manually vary the speed of travel of the carriage along the guide by a certain percentage, and in which the parameters of the oscillation of the welding torch are automatically matched to these variations of the speed of travel of the carriage.
These and other objects which will be clear to those skilled in the art are achieved with a device according to the attached claims.